The present invention relates to a silver halide photographic light-sensitive material, particularly to a silver halide photographic light-sensitive material improved in image quality, storage stability and pressure resistance and a silver halide photographic emulsion used in said light-sensitive material.
In recent years, there is a growing demand for a higher image quality in a silver halide color photographic light-sensitive material.
To meet the requirement for improved color reproducibility, a variety of studies have been made on development-inhibiting action between layers of different color sensitivities (inter-image effect).
In a color reversal light-sensitive material, studies have been made on enhancement of the inter-image effect in each of the first development (black and white development) and the second development (color development).
With respect to the second development, there is known a technique to incorporate a compound capable of releasing a developing inhibitor upon development, such as a DIR coupler, into a light-sensitive material; but, its effect is not satisfactory.
With respect to the first development, there have been proposed to incorporate a compound capable of releasing a developer upon development into a light-sensitive material. For example, DIR-hydroquinones are described in Japanese Patent Publication Open to Public Inspection No. 129536/1974 and U.S. Pat. Nos. 3,379,529, 3,620,746, 4,332,878, 4,377,634; DIR-aminophenols are described in Japanese Patent O.P.I. Publication No. 57828/1977; and p-nitrobenzyl derivatives are described in EP No. 45129.
Further, Japanese Patent O.P.I. Publication No. 213847/1986 discloses a compound which releases a photographically useful fragment while inducing an intramolecular oxidation-reduction reaction as a redox compound.
However, these compounds were not effective enough to improve the quality of images, in addition to a drawback of lowering the shelf-life of a light-sensitive material.
Regarding the 1st development, it is known that an inter-image effect which utilizes iodide ions released by development is useful. For example, techniques which use a fogged emulsion or an internally-fogged emulsion are disclosed in Japanese Patent Examined Publication No. 35011/1974 and Japanese Patent O.P.I. Publication No. 91946/1987. But, these techniques have a drawback of needing a larger amount of silver. Similarly, the inter-image effect using iodide ions can also be achieved by controlling the silver halide composition or silver halide grain structure in a silver halide emulsion of color sensitive layer. A proposal is made to use a tabular silver halide emulsion having a grain-diameter-to-grain-thickness ratio (aspect ratio) of 5 or more in Japanese Patent O.P.I. Publication Nos. 285549/1988 and 305355/1988. However, these techniques are still insufficient in providing satisfactory results, and a further improvement is strongly desired.
Generally, a silver halide used in a silver halide color photographic light-sensitive material is formed into grains, and then subjected to chemical sensitization for enhancing sensitivity and to spectral sensitization so as to be sensitive to light of a specific wavelength range.
A silver halide emulsion prepared as the above is subsequently coated on a support, using gelatin as a main binder, together with photographic additives such as a coupler, dye, etc. and dried to form a silver halide color photographic light-sensitive material. Said light-sensitive material is then exposed imagewise and developed to obtain desired images. But when a light-sensitive material is left unused for a long time from its preparation to imagewise exposing or exposed to a humid and hot atmosphere, generation of fog, desensitization and disordered gradation is observed at times.
This is attributed to change in a state of adsorption or desorption of various photographic additives, such as a sensitizing dye, chemical sensitizer, antifogging agent, development inhibitor and latent image stabilizer, which are adsorbed to the surface of silver halide grains.
To improve storage stability of such materials, studies have been made on selection of additive, improvement of addition method and adjustment of addition amount. But, an alteration of a type of silver halide requires an adjustment each time; besides, these approaches are not so effective.
Among silver halide emulsions, one which comprises regular crystals has a relatively good storage stability, but it tends to be affected by other silver halide grains contained in an adjacent layer; moreover, for its high sensitivity, the storage life is also liable to be lowered when a silver iodide content is raised.
Besides photographic properties such as sensitivity, gradation, image quality; and preservability of a fresh and developed materials; physical properties of a silver halide photographic light-sensitive material must be good enough to be handled. A light-sensitive material is subjected to pressure under various conditions in the course of manufacturing and distribution, or inside of exposing equipment or developing equipment. Generally, silver halides contained in a light-sensitive material lose their normal photographic characteristics when subjected to pressure, causing desensitization, sensitization at times, or fogging. Examples of such troubles are described in J.S.P. 2, 105 (1954) by P. Faelens et al.; J. Opt. Soc. Am. 38 1054 (1948) by K. B. Mather; and J.P.S. 4, 33, 127 (1985) by R. King et al.
When a light-sensitive material is pressed, scratched or rubbed on the surface, or subjected to folding or cutting, neighboring silver halide grains are pressed and yield an image density not corresponding to a given imagewise exposure, thereby quality of a finished image is impaired.
While pressure resistance can be improved to some extent by modifying a support which constitutes a light-sensitive material or a binder (gelatin and other hydrophilic polymers) which holds silver halides, it is largely depending on characteristics of silver halide grains.
For the improvement of the pressure resistance, studies have been made on various aspects such as halide composition of silver halide, halide distribution, method of chemical ripening, doping of metallic ions, selection of a sensitizing dye. But, most of the outcomes are accompanied with desensitization and inadequate for practical uses.